DS Explanation is confusing me!

[richs_ca]

If a and b are positive integers, is 2 (Sq.rt of a+b) > 4(sq.rt of b)?

1) b > 3a
2) a + b > 3

The answer explanation says that i should simplify the problem by dividing by 2 and then to square both sides to get a + b > 4b.

However, I had always thought that if you divide one side by 2, you would need to do the same to the other side so it would be a + b > 2b.

So now I'm a little lost.

Help?

Thanks!!

[simplyjat]

You missed squaring 2 on the right hand side of the equation

2(sqrt(a+b)) > 4(sqrt(b))
=> sqrt(a+b) > 2(sqrt(b)) {dividing both sides by 2}
=> a+b > 4b {taking square of both sides}

[Neo2000]

When you divide by 2 on both sides you get

(Sq.rt of a+b) > 2(sq.rt of b)

If you square this you get a+b > 4b

[richs_ca]

Ah ha!! Got it - and it now seems so obvious.

Thank you very much!

[gmat765]

and now it becomes clear